 production in proton-nucleus and indium-indium collisions Michele Floris University and INFN, Cagliari, Italy. on behalf of the NA60 Collaboration ISMD.

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Presentation on theme: " production in proton-nucleus and indium-indium collisions Michele Floris University and INFN, Cagliari, Italy. on behalf of the NA60 Collaboration ISMD."— Presentation transcript:

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14/08/2005ISMD Peripheral Bin Peripheral bin studied in three p T bins  The normalizations of the hadron decay cocktail and of the continuum are independently fit in each p T bin   and  ratios are nearly p T independent  The peripheral bin is well described in terms of expected sources but: “Too many” low p T  mesons Peripheral In-In is not quite pp, it’s more like CC or OO Effect of pion annhilation cannot be neglected

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14/08/2005ISMD  /  comparison to NA50  A direct comparison is impossible, due to the contribution from pion annihilation, which must be even higher in Pb-Pb collisions, and which NA50 cannot isolate NA50 points converted to the window p T >1.1 GeV/c assuming T=228 MeV      used (lower limit for NA50  ratio)

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14/08/2005ISMD  /  comparison to NA49  /  Same trend as a function of N part  constant If we set the ratio  to 0.07–0.08, as suggested by statistical models, then the NA60   yield is a factor 1.5–2 higher than the NA49 value

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14/08/2005ISMD  transverse momentum spectrum We select the events on the  peak and use two side mass windows to estimate the p T distribution of the continuum under the peak Then we correct for the acceptance, calculated (by Monte Carlo) as a 2-dim matrix: p T and y background total 

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14/08/2005ISMD There is no significant variation of the extracted inverse slope parameter, T, with rapidity There is a clear increase from peripheral to central collisions With full statistics, extension up to p T > 3 GeV/c should be feasible  p T spectrum versus y and centrality

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14/08/2005ISMD Summary NA60 is well suited to help understanding the “  puzzle”  New In-In measurements  Better p T coverage than previous  experiments  Capability to measure   KK  ratio:  Rise with N part consistent with NA49 and NA50  Absolute values between NA49 and NA50 Inverse slope T of the  p T -distribution:  Agreement between NA49 and NA60  The difference between NA49 and NA50 is not due to the different channels probed   KK  Full MC simulation shows the feasibility of the study  Final tuning still needed for background subtraction in real data

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14/08/2005ISMD hadron absorber and trackingmuon trigger magnetic field iron wall muon other targets Concept of NA60: place a silicon tracking telescope in the vertex region to measure the muons before they suffer multiple scattering in the absorber and match them to muon measured in the spectrometer  Improved kinematics (~20 MeV/c 2 at  instead of 80 MeV/c 2 in NA50) Origin of muons can be accurately determined 2.5 T dipole magnet beam tracker vertex tracker Concept of NA60

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14/08/2005ISMD A certain fraction of muons is matched to closest non-muon tracks (fakes). Only events with  2 < 3 are selected. Fake matches are subtracted by a mixed-events technique (CB) and an overlay MC method (only for signal pairs, see below) Matching between the muons in the Muon Spectrometer (MS) and the tracks in the Vertex Telescope (VT) is done using the weighted distance (  2 ) in slopes and inverse momenta. For each candidate a global fit through the MS and VT is performed, to improve kinematics. Muon track matching

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14/08/2005ISMD Mass spectrum in semi-central In-In collisions Complicated continuum under the  in more central collisions However, the excellent mass resolution of NA60 allows us to extract a robust  yield